examples/dtls-echo: set address family for sessions

[miri64]

Contribution description

d424aae introduced address families to the RIOT interpretation of tinydtls-session_ts. However, while fixing the naming for the addr field, it did not set the family member for the sessions in the dtls-echo example, having that example run into an assertion. This patch fixes that.

Testing procedure

I used the same script to find the issue to test its fix (assuming you are in RIOTBASE:

sudo dist/tools/tapsetup/tapsetup
cat << EOF > test_dtls.py
#! /usr/bin/env python3
import sys

from riotctrl.ctrl import RIOTCtrl

sys.path.append("dist/pythonlibs")
from riotctrl_shell.netif import IfconfigListParser, Ifconfig

if __name__ == "__main__":
    RIOTCtrl.MAKE_ARGS = ("-j",)
    ctrl0 = RIOTCtrl(application_directory="examples/dtls-echo", env={"WERROR": "0"})
    ctrl1 = RIOTCtrl(
        application_directory="examples/dtls-echo", env={"PORT": "tap1", "WERROR": "0"}
    )
    ctrl0.make_run(["flash"])
    with ctrl0.run_term(reset=False), ctrl1.run_term(reset=False):
        ctrl0.term.logfile = sys.stdout
        ctrl1.term.logfile = sys.stdout
        shell0 = Ifconfig(ctrl0)
        shell1 = Ifconfig(ctrl1)
        netifs = IfconfigListParser().parse(shell1.ifconfig_list())
        server_addr = list(netifs.values())[0]["ipv6_addrs"][0]["addr"]
        res = shell1.cmd("dtlss start")
        assert res.strip() == "dtlss start"
        res = shell0.cmd(f"dtlsc {server_addr} hello")
        res1 = shell1.cmd("help")
        assert "Client: got DTLS Data App -- hello --" in res
EOF
chmod +x test_dtls.py
./test_dtls.py

It should succeed and its output should contain the following crucial lines:

> dtlsc fe80::d827:1dff:fea8:6424 hello
dtlsc fe80::d827:1dff:fea8:6424 hello
Client: got DTLS Data App -- hello --
> help

Server: got DTLS Data App: --- hello ---	(echo!)

Issues/PRs references

Follow-up on #17765

[maribu]

ACK. Code looks good, trusting your testing

[miri64]

Backport provided in #18371